Retention force of removable partial dentures with different double crowns

The aim of the study was to compare the retentive behaviors of double crowns with different designs and material compositions before and after artificial aging.

Six pairs of double crowns were fabricated: telescopic crowns 0° made of high-noble metal (group A) or non-precious metal (group B), telescopic zirconia copings with secondary crowns made of electroplated gold 2° (group C), crowns with friction pins 2° made of non-precious metal (group D) or zirconia (group E), and conical crowns 6° made of high-noble metal (group F). Retention forces were assessed before and after artificial aging, and after axial and non-axial loading.

Initially, specimens in group D (13.9 N), B (12.5 N), and E (12.2 N) exhibited the highest retention forces. Retention forces in groups A (9.6 N), C (7.4 N), and F (6.0 N) were statistically significantly lower than those of the other groups (p < 0.05). After artificial aging, double crowns with additional retention elements exhibited the highest retention forces. The largest retention force losses were evident in groups A (70%), B (64%), C (39%), and F (47%).

Double crowns with different designs and made of different materials exhibited different retention forces and different long-term retentive behavior. The highest retention force losses were evident in double crowns with more extended surface contact, such as telescopic crowns.

Telescopic crowns with additional retention elements were more resistant to wearing than double crowns without additional retention elements. An additional clinical benefit might be the quick and easy possibility of enhancing retention.